The present invention relates to planetary transmissions and, more particularly, to a family of planetary transmissions providing at least six forward speed ratios and a reverse speed ratio utilizing three planetary gearsets and five torque-transmitting mechanisms.
Passenger vehicles include a powertrain that is comprised of an engine, multi-speed transmission, and a differential or final drive mechanism. The multi-speed transmission increases the overall operating range of the vehicle by permitting the engine to operate through its torque range a number of times as the transmission ratios are interchanged. The number of forward speed ratios that are available in a transmission determines the number of ratio interchanges that can occur and therefore the number of times the engine torque range can be repeated.
Early automatic transmissions had two speed ranges. This severely limited the overall speed range of the vehicle and therefore required a relatively large engine that could produce a wide speed and torque range. This resulted in the engine operating at a specific fuel consumption point, during cruising, other than the most efficient point. Therefore, manually shifted (countershaft transmissions) were the most popular.
With the advent of three and four speed automatic transmissions, the automatic shifting (planetary gear) transmission increased in popularity with the motoring public. These transmissions improve the operating performance and fuel economy of the vehicle. The increased number of speed ratios reduces the step size between ratios and therefore improves the shift quality of the transmission by making the ratio interchanges substantially imperceptible to the operator under normal vehicle acceleration.
It has been suggested that the number of forward speed ratios be increased to five and even six speeds. This has been accomplished in many heavy truck powertrains. Six speed transmissions are disclosed in U.S. Pat. No. 4,070,927 issued to Polak on Jan. 31, 1978; U.S. Pat. No. 6,071,208 issued to Koivunen on Jun. 6, 2000; U.S. Pat. No. 5,106,352 issued to Lepelletier on Apr. 21, 1992; U.S. Pat. No. 5,599,251 issued to Beim and McCarrick on Feb. 4, 1997, U.S. Pat. No. 6,083,135 issued to Baldwin et al. on Jul. 4, 2000, and European Patent Application No. EP 1 033 510 A1 published Jun. 9, 2000.
Six speed transmissions offer several advantages over four and five speed transmissions, including improved vehicle acceleration and improved fuel economy. While many trucks employ six-speed transmissions, such as Polak, passenger cars are still manufactured, for the main part, with three and four speed automatic transmissions, and relatively few five or six speed devices due to the size and complexity of these transmissions. The Polak transmission provides six forward speed ratios with three planetary gearsets, two clutches, and three brakes. The Koivunen and Beim patents utilize six torque transmitting devices including four brakes and two clutches to establish the six forward speed ratios and one reverse ratio. The Lepelletier and the EP publications each employ three planetary gearsets, three clutches and two brakes to provide six forward speed ratios and one reverse ratio. One of the planetary gearsets in each of these publications is positioned and operated to establish two fixed speed input members for the remaining two planetary gearsets.
It is an object of the present invention to provide an improved family of transmissions providing six forward speed ratios and one reverse speed ratio.
In one aspect of the present invention, each of the family members incorporates three planetary gearsets and five selectively engageable torque-transmitting mechanisms.
In another aspect of the present invention, each of the planetary gearsets has three planetary members with a first member of the first planetary gearset being continuously interconnected with a first member of the second planetary gearset, and a first member of the third planetary gearset.
In another aspect of the present invention, a second interconnecting member continuously interconnects a second member of the first planetary gearset with a second member of the second planetary gearset.
In still another aspect of the present invention, a second member of the third planetary gearset is continuously connected with a stationary member of the transmission, such as a transmission case or housing.
In yet still another aspect of the present invention, a transmission output shaft is continuously connected with at least one member of one of the planetary gearsets.
In another aspect of the present invention, an input shaft is selectively connectible with the planetary gearsets through three selectively engageable torque-transmitting mechanisms.
In a further aspect of the present invention, a first of the five torque-transmitting mechanisms selectively interconnects the input shaft with a member of the first or second planetary gearset.
In a yet further aspect of the present invention, a second of the torque-transmitting mechanisms selectively interconnects the input shaft with at least one member of one of the planetary gearsets.
In still a further aspect of the present invention, a third of the torque-transmitting mechanisms selectively interconnects the input shaft with at least one member of the first, second, or third planetary gearsets.
In yet still a further aspect of the present invention, a fourth of the torque-transmitting mechanisms provides either a selective connection between the transmission housing and at least one member of the planetary gearsets, or a selective interconnection between a member of one of the planetary gearsets with another member of one of the planetary gearsets.
In a further aspect of the present invention, a fifth of the torque-transmitting mechanisms selectively interconnects a member of one of the planetary gearsets with a stationary housing or transmission case.
In still a further aspect of the present invention, the five torque-transmitting mechanisms are selectively engageable in combinations of two to at least establish six forward speed ratios and one reverse speed ratio between the input shaft and the output shaft of the transmission.